Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2131: A 35 year old man presents to an emergency department with an exquisitely tender prostate gland. An acute bacterial infection is suspected. Which of the following organisms is the most common pathogen in this setting?

A. Enterobacter
B. Escherichia (Correct Answer)
C. Klebsiella
D. Proteus

Explanation: ***Escherichia*** - **_Escherichia coli_** is the most common Gram-negative bacillus responsible for both acute and chronic bacterial prostatitis due to its prevalence in the normal gut flora and its ability to ascend the urinary tract. - It accounts for approximately **80% of all acute bacterial prostatitis cases** because of its uropathogenic factors like fimbriae that allow adherence to urinary epithelial cells. *Enterobacter* - While **_Enterobacter_ species** can cause urinary tract infections and prostatitis, they are significantly less common than _E. coli_. - Prostatitis due to _Enterobacter_ often occurs in **hospitalized patients** or those with complicated UTIs, not typically in a healthy 35-year-old in the community. *Klebsiella* - **_Klebsiella pneumoniae_** is another Gram-negative rod that can cause prostatitis, frequently in patients with **urinary tract abnormalities** or catheterization. - It is less common than _E. coli_ in community-acquired acute bacterial prostatitis and is often associated with more severe disease or resistance patterns. *Proteus* - **_Proteus mirabilis_** is known for its ability to produce **urease**, which can lead to struvite stone formation in the urinary tract, and can cause UTIs. - While it can cause prostatitis, it is much **less frequent than _E. coli_** and often associated with urinary calculi or long-term catheter use.

Question 2132: BPF (Brazilian purpuric fever) is caused by:

A. Salmonella
B. H.influenzae biotype aegyptius (Correct Answer)
C. V. cholerae
D. None of the options

Explanation: ***H.influenzae biotype aegyptius*** - **Brazilian purpuric fever (BPF)** is a severe, acute pediatric disease characterized by **fever, purpura, vascular collapse, and high mortality**, specifically caused by this distinct strain of *Haemophilus influenzae biotype aegyptius*. - The infection typically starts as a **conjunctivitis** caused by the same organism, which then disseminates, leading to the systemic symptoms of BPF. *Salmonella* - *Salmonella* species are typically associated with **gastroenteritis**, **typhoid fever**, or other systemic infections, but not Brazilian purpuric fever. - While *Salmonella* can cause severe infections in children, its clinical presentation and typical symptoms (e.g., diarrhea, enteric fever) differ significantly from BPF. *V. cholerae* - *Vibrio cholerae* is the causative agent of **cholera**, an acute diarrheal illness characterized by severe watery diarrhea and dehydration. - It does not cause the purpuric rash, vasculitis, or the specific sudden onset and high mortality seen in Brazilian purpuric fever. *None of the options* - This option is incorrect because *H.influenzae biotype aegyptius* is the established and specific cause of Brazilian purpuric fever. - The disease is well-defined with a particular etiology, making "none of the options" an invalid choice.

Question 2133: Most common causative organism for bacterial meningitis beyond 3 years of age is -

A. H. influenzae Type b
B. Pneumococcus (Correct Answer)
C. Meningococcus
D. Staphylococcus aureus

Explanation: ***Pneumococcus*** - *Streptococcus pneumoniae* (Pneumococcus) is currently the most common cause of **bacterial meningitis** in individuals older than 3 years, particularly after the widespread use of the HiB vaccine. - It frequently causes severe disease with **high mortality and morbidity** due to its ability to colonize the nasopharynx and invade the bloodstream and meninges. *H. influenzae Type b* - Before the introduction of the **HiB vaccine**, *Haemophilus influenzae* type b was the leading cause of bacterial meningitis in children under 5 years of age. - Due to **routine vaccination**, its incidence has dramatically decreased, making it less common now in children beyond 3 years. *Meningococcus* - *Neisseria meningitidis* (Meningococcus) is a significant cause of bacterial meningitis, particularly in **epidemics** and in young adults and adolescents. - While it causes outbreaks and serious disease, it is generally less common than pneumococcal meningitis beyond childhood in areas with high vaccination coverage. *Staphylococcus aureus* - *Staphylococcus aureus* can cause bacterial meningitis but is more often associated with **neurosurgical procedures**, head trauma, or indwelling medical devices, rather than being a primary community-acquired pathogen for meningitis in immunocompetent individuals. - It is not the most common causative organism for community-acquired bacterial meningitis in the general population beyond 3 years of age.

Question 2134: A major step in the pathogenesis of listeriosis is?

A. The antiphagocytic activity of the L. monocytogenes capsule
B. The release of hyaluronidase by L. monocytogenes, which contributes to its dissemination from local sites
C. The formation of antigen-antibody complexes with resultant complement activation and tissue damage
D. The survival and multiplication of L. monocytogenes within mononuclear phagocytes and host epithelial cells (Correct Answer)

Explanation: ***The survival and multiplication of L. monocytogenes within mononuclear phagocytes and host epithelial cells*** - **Listeria monocytogenes** is a **facultative intracellular bacterium** that primarily infects and replicates within **macrophages** and epithelial cells. This intracellular survival helps it evade the host immune system and spread from cell to cell. - Its ability to induce its own uptake (**internalin-mediated uptake**), escape the phagosome (via **listeriolysin O**), and move within the cytoplasm (via **ActA protein** for actin polymerization) are key to its pathogenesis and evasion of humoral immunity. *The antiphagocytic activity of the L. monocytogenes capsule* - While some bacteria use capsules for antiphagocytic activity, **Listeria monocytogenes** is not known for having a significant capsule as a primary virulence factor. - Its main strategy for evading phagocytosis involves **intracellular survival** rather than external camouflage. *The release of hyaluronidase by L. monocytogenes, which contributes to its dissemination from local sites* - **Hyaluronidase** is an enzyme produced by some bacteria to break down hyaluronic acid in connective tissue, aiding in spread, but it is not a major virulence factor for **Listeria monocytogenes**. - Listeria primarily disseminates through its **intracellular movement** and cell-to-cell spread, rather than extensive extracellular enzyme activity for tissue degradation. *The formation of antigen-antibody complexes with resultant complement activation and tissue damage* - This mechanism describes **Type III hypersensitivity reactions**, which involve the deposition of immune complexes leading to inflammation and tissue damage. - While immune responses occur during listeriosis, this particular mechanism is not a major or primary step in the **pathogenesis** of the initial infection and spread of **Listeria monocytogenes**.

Question 2135: Most common cause of Acute epiglottitis in the pre-vaccine era was

A. Haemophilus influenzae A
B. Respiratory Syncytial Virus
C. Parainfluenza virus
D. Haemophilus influenzae B (Correct Answer)

Explanation: ***Haemophilus influenzae B*** - **Historically**, *Haemophilus influenzae type B* (Hib) was the **most common bacterial cause of acute epiglottitis**, especially in children, accounting for >90% of cases in the pre-vaccine era. - The introduction of the **Hib vaccine** (starting in the 1990s) has **dramatically reduced the incidence** of Hib-related epiglottitis by >95%. - **Currently**, in the post-vaccine era, other pathogens like *Streptococcus pyogenes*, *S. pneumoniae*, and *S. aureus* are more common causes, though Hib may still occur in unvaccinated individuals. *Haemophilus influenzae A* - *Haemophilus influenzae type A* is occasionally associated with invasive infections but was **not the predominant cause** of acute epiglottitis even historically. - It lacks the same epidemiological significance as type B in causing epiglottitis. *Respiratory Syncytial Virus* - **Respiratory Syncytial Virus (RSV)** is a primary cause of **bronchiolitis and pneumonia** in young children. - It is **not associated with epiglottitis**, which is a distinct condition involving supraglottic inflammation. *Parainfluenza virus* - **Parainfluenza viruses** are a common cause of **croup (laryngotracheobronchitis)**, characterized by subglottic inflammation and a "barking" cough. - While it affects the upper airway, it **does not cause epiglottitis**, which involves the supraglottic structures.

Question 2136: A patient with colorectal cancer develops septicemia complicated by endocarditis. You would expect the blood cultures to grow?

A. Streptococcus agalactiae
B. Streptococcus pyogenes
C. Streptococcus bovis (Correct Answer)
D. Streptococcus pneumoniae

Explanation: ***Streptococcus bovis*** - **Streptococcus bovis** (now often referred to as *Streptococcus gallolyticus subsp. gallolyticus*) is strongly associated with **colorectal cancer** and can cause **bacteremia** and **infective endocarditis**. - Its presence in blood cultures, particularly in cases of endocarditis, should prompt a workup for underlying colorectal malignancy. *Streptococcus agalactiae* - This organism, also known as **Group B Streptococcus (GBS)**, is a common cause of **neonatal sepsis** and meningitis, and can cause infections in immunocompromised adults, but it does not have a specific association with colorectal cancer. - While it can cause endocarditis, it is not the most likely causative agent in a patient with colorectal cancer. *Streptococcus pyogenes* - **Streptococcus pyogenes** (Group A Streptococcus or **GAS**) is known for causing **pharyngitis** ("strep throat"), **scarlet fever**, **rheumatic fever**, and **necrotizing fasciitis**. - It is not typically associated with chronic conditions like colorectal cancer or with endocarditis in this specific context. *Streptococcus pneumoniae* - **Streptococcus pneumoniae** is a leading cause of **pneumonia**, **otitis media**, **meningitis**, and **sepsis**, particularly in young children and the elderly. - While it can cause endocarditis, there is no direct link between *S. pneumoniae* infection and underlying colorectal cancer.

Question 2137: Carrion's disease is caused by:

A. Bartonella henselae
B. Bartonella quintana
C. Bartonella bacilliformis (Correct Answer)
D. Bartonella washoensis

Explanation: ***Bartonella bacilliformis*** - **Carrion's disease**, also known as **Bartonellosis**, is exclusively caused by the bacterium **Bartonella bacilliformis**. - This disease manifests in two distinct stages: an acute phase (**Oroya fever**) characterized by severe anemia, and a chronic eruptive phase (**verruga peruana**) with skin lesions. *Bartonella henselae* - This bacterium is primarily responsible for **Cat-scratch disease** and can also cause **bacillary angiomatosis**, endocarditis, and trench fever-like syndrome. - It is typically transmitted to humans through scratches or bites from infected cats. *Bartonella quintana* - This species is the causative agent of **trench fever**, a louse-borne illness, and can also lead to **bacillary angiomatosis**. - Trench fever is characterized by recurrent fevers, headache, body aches, and sometimes a rash. *Bartonella washoensis* - **Bartonella washoensis** is a less common species primarily associated with **myocarditis** and endocarditis in humans. - Infections with this bacterium are often linked to exposure to rodents, particularly ground squirrels.

Question 2138: Subdural empyema is most commonly caused by:

A. Staphylococcus aureus
B. Streptococcus pneumoniae (Correct Answer)
C. H. influenzae
D. E. coli

Explanation: ***Streptococcus pneumoniae*** - **_Streptococcus species_**, including **_S. pneumoniae_**, aerobic and anaerobic streptococci, and S. milleri group, are the **most common causative organisms** of **subdural empyema**, accounting for **60-70% of cases**. - **Subdural empyema** most frequently arises from **paranasal sinusitis** (50-80% of cases) or **otitis media/mastoiditis**, infections typically caused by **streptococcal species**. - The polymicrobial nature of sinus and ear infections explains why **streptococci** predominate in subdural empyema. *Staphylococcus aureus* - **_Staphylococcus aureus_** is an important cause of **subdural empyema**, particularly in **post-neurosurgical cases** and following **penetrating head trauma**. - It accounts for approximately **10-20% of cases** but is **not the most common** overall pathogen. - When subdural empyema follows **surgery** or **direct inoculation**, S. aureus becomes more likely than in community-acquired cases. *H. influenzae* - **_Haemophilus influenzae_** was historically significant before widespread **Hib vaccination**. - Currently uncommon as a cause of **subdural empyema**, especially in vaccinated populations. - May still be seen in unvaccinated individuals or those with underlying immunodeficiency. *E. coli* - **_E. coli_** is a rare cause of **subdural empyema** in adults. - More relevant in **neonatal meningitis** and infections in **immunocompromised hosts**. - Gram-negative bacilli are generally uncommon in subdural empyema compared to gram-positive cocci.

Question 2139: Bartonella henselae causes which disease -

A. Spirillum fever
B. Chancre redux
C. Bacillary peliosis (Correct Answer)
D. Rat bite fever

Explanation: ***Bacillary peliosis*** - **Bartonella henselae** is a gram-negative rod that causes **bacillary peliosis** (peliosis hepatis), particularly in immunocompromised individuals such as AIDS patients. - This condition is characterized by **blood-filled cystic spaces** in the liver and spleen. - *Note: Bartonella henselae* most commonly causes **Cat Scratch Disease** in immunocompetent individuals, but bacillary peliosis is the specific disease entity among the given options. *Spirillum fever* - **Spirillum fever** is caused by **Spirillum minus** (a different bacterial genus) and is characterized by a relapsing fever after a rat bite. - Its clinical presentation and causative agent differ from those of *Bartonella henselae* infections. *Chancre redux* - **Chancre redux** is not a standard medical term and does not represent a recognized disease entity. - It does not correspond to any disease caused by *Bartonella henselae*. *Rat bite fever* - **Rat bite fever** is caused by either **Streptobacillus moniliformis** or **Spirillum minus**, both of which are distinct from *Bartonella henselae*. - While *Bartonella henselae* is transmitted by cat scratches or bites, it does not cause rat bite fever.

Question 2140: Which of the following statement is false regarding bacterial cell wall?

A. Region II of LPS is core polysaccharide (Correct Answer)
B. Cell wall of Gram-positive bacteria is thicker than that of Gram-negative bacteria
C. LPS is responsible for O antigen specificity of Gram-negative bacteria
D. Lipopolysaccharide is present in the outer membrane of Gram-negative bacteria

Explanation: ***Region II of LPS is core polysaccharide*** - This statement is **false** because **Region II of LPS (Lipopolysaccharide) is the O antigen (or O polysaccharide)**, which is the outermost and most variable part of LPS. - The **core polysaccharide is Region I**, located between Lipid A and the O antigen. - **LPS structure**: Lipid A (Region 0) → Core polysaccharide (Region I) → O antigen (Region II). *Cell wall of Gram-positive bacteria is thicker than that of Gram-negative bacteria* - This is **true**. **Gram-positive** bacteria have a **thick peptidoglycan layer** (20-80 nm), substantially thicker than Gram-negative bacteria. - **Gram-negative** bacteria have a **thin peptidoglycan layer** (2-7 nm) located in the periplasmic space between inner and outer membranes. *LPS is responsible for O antigen specificity of Gram-negative bacteria* - This is **true**. The **O antigen** (or O polysaccharide) is the outermost part of the LPS molecule and is responsible for the **serotypic specificity** of Gram-negative bacteria. - This region is highly variable and is used for **immunological identification** of different bacterial strains. *Lipopolysaccharide is present in the outer membrane of Gram-negative bacteria* - This is **true**. **LPS is a major component of the outer membrane** of Gram-negative bacteria, located in the outer leaflet of the outer membrane. - LPS consists of three regions: **Lipid A** (endotoxin), **core polysaccharide**, and **O antigen**.

Practice by Chapter

Staphylococci

Practice Questions

Streptococci and Enterococci

Practice Questions

Neisseria and Moraxella

Practice Questions

Corynebacterium and Listeria

Practice Questions

Bacillus and Clostridium

Practice Questions

Enterobacteriaceae

Practice Questions

Vibrio, Aeromonas, and Plesiomonas

Practice Questions

Pseudomonas and Related Bacteria

Practice Questions

Haemophilus and HACEK Group

Practice Questions

Bordetella and Brucella

Practice Questions

Mycobacteria

Practice Questions

Spirochetes

Practice Questions

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